(4) The last use to which the Wadi Raiân might be put, and which has lately been suggested, is to adapt it for the reception of the drainage waters of the Nile Valley, after the basin area of at least Middle Egypt has been converted into Sêfi (summer) irrigation by means of the increased supply provided by the assumed existence of reservoirs in the Upper Nile Valley and a regulating dam at Asyût. When all these basin lands are converted into tracts under perennial irrigation, there will be a great difficulty in the disposal of their drainage water during the time of high flood, and the Wadi Raiân affords a possible means of solving this problem. Even though the drainage might gain on evaporation and the Wadi Raiân become eventually full, its water surface could be annually so far lowered by allowing a flow out into the Nile during the summer months, as to prepare the basin for the reception of all the drainage it would be called upon to receive during the next flood season. It would further be possible to combine the uses Nos. 2 and 4, and make the depression serve both as a receptacle of the drainage during the floods and a reservoir to supplement the Low Nile during summer. But it might be objected that the admixture of drainage with the reservoir waters, returned to the Nile in summer, might render the river water unfit for irrigation. Supposing the drainage discharge, which must be received into the reservoir, amounts to 15 million cubic metres a day for 80 days (probably a high estimate), the total volume of drainage water would amount to 1200 million cubic metres, or one-third of the quantity of water (3600 million cubic metres) required to fill the lake from R.L. 21 to 26, or half of the 2400 million cubic metres returned to the Nile Valley. This would be further diluted by the summer discharge of the Nile itself, to which it would be added. If the reservoir were filled to R.L. 25 during the flood months by the drainage and flood waters together, the remaining metre could be added by a canal discharging 7 million cubic metres a day for 100 days in winter, and fed from the Ibrahimîyah Canal, or a new branch of it, which would replace the Bahr Yûsuf, when the latter was converted into the main drainage line consequent on the basin lands being brought under perennial irrigation. If then the drainage water should not be found salt enough to seriously affect the quality of the reservoir water, the Wadi Raiân might be made to serve both the purposes stated.